The line widths of circuit patterns are being reduced more and more due to the downscaling of semiconductor devices. The wavelengths of the exposure light of lithography technology used to expose resist films are being shortened to respond to the need for such reductions. So-called extreme ultraviolet (EUV) exposure light in wavelength regions around 13.5 nm is being investigated for use in generations having pattern widths of 30 nm or less. It is thought that EUV light will enable reductions of the pattern width and the pattern pitch not achievable conventionally.
Because EUV light attenuates rapidly in the atmosphere, the entire EUV optical path must be in a vacuum atmosphere. Therefore, the entire exposure unit including the EUV light source, the reticle stage holding the reticle, the optical system, the wafer stage holding the wafer to be exposed, and the like is disposed inside the vacuum chamber. In such a case, an electrostatic chuck is used because a vacuum chuck cannot be used by the reticle stage to hold the reticle. In other words, the entire back face of the reticle is held by and electrostatic charge of the chuck surface of the reticle stage (for example, refer to JP-A 2002-299228 (Kokai)).
Ultra-fine recesses/protrusions are formed in the electrostatic chuck surface of the reticle stage. In the case where such a reticle stage is used repeatedly, protrusions of the ultra-fine recesses/protrusions wear and particles undesirably occur. In the case where particles exist on the electrostatic chuck surface of the reticle stage, the particles are interposed between the reticle stage and the back face of the reticle when a new reticle is mounted; and the reticle undesirably deflects. As a result, the flatness of the reticle front face decreases and errors such as focus shift occur. Further, particles that move around to the reticle front face become foreign objects interposed in the optical path; and defects are undesirably transferred onto the wafer. Therefore, in the case where particles occur on the chuck surface of the reticle stage, it is necessary to clean the reticle stage promptly.
However, because the exposure unit including the reticle stage is disposed inside the vacuum chamber as described above, the interior of the vacuum chamber must be opened to the atmosphere to clean the reticle stage. Once the interior of the vacuum chamber is opened to the atmosphere, about half a day to a whole day is necessary to increase the degree of vacuum enough to start exposing again. Meanwhile, the exposure processing is stopped. As a result, the substantial operation time of the exposure apparatus is shortened; and the throughput of the semiconductor device undesirably decreases.